31.With irrigation came surplus food，which meant that large numbers of people were freed trom the land to pursue nonagrarian specialities—technological development，scholarship for its sake——and war。
随着有了灌溉，粮食就有了剩余，这就意味着大批人就可解脱出来从事农业以外的工作一发展工艺，研究其学问——甚至参加战争。 (with...“随着”，引导的短语作状语。
With the approach of sunset it became chilly，come surplus food是倒装语序，food是主语，came是谓语。which引导特种定语从句，指上句话。不定式to pursue..。war有结果状语的意味。).
32.First of all， Kepler found that each planet goes around the sun in a curve called an ellipse，with the sun at a focus of the ellipse.
开普勒首先发现了每个行星都以椭圆曲线绕太阳运行，太阳则位于椭圆的焦点。(with the sun at，..为介词复合结构作状语，补充说明。).
33.It should be noted that a rocket does not depend on the atmosphere for its propulsion，but would actually perform better in the absence of an atmosphere becauseOf lessened air resistance.
应该注意，火箭的推力与大气无关，在没有大气的情况下，由于空气阻力减小，火箭实际上会运行得更好。(in the absence of anatmosphere含有虚拟条件的意味。).
34.Electrical power is always carried over long distances as a high-tension current at low-currentstrength.It is also sent as an alternating current，for such current is comparatively easily transformed eitherup ordown in voltage.
电力总是以高电压低电流的方式进行远距离输送的，又是以交流电的形式送电的，因为这种交流电易于升压或降压。(两个as构成的介词短语都用作方式方法状语，分别说明iscarried和issent。).
35.When one considers the immense change in the size and reliability of computers and all other electronic devices that has taken place，it is clean that computers for doing this type of control of movement according to sense impression will certainly be available.
当我们考虑到计算机和其他所有电子器件在尺寸和可*性方面所发生的极大变化时，就不难明白，根据感觉进行这类活动控制的计算机一定会出现。(for...movement是computers的定语，介词短语according to sense impression作状语，说明动名词doing。).
36。In l664 the great English diarist，John Evelyn，published，with the approval of the Royal Society of London，a book Sylva or a Discourse of Forest Trees in which one sees，perhaps for the first time，a realization that trees，then so important in the construction of ships，were indeed becoming sadly depleted and that something urgently needed to be done by way of deliberate planting to ensure enough for the future.
1664.年，英国伟大的日记作家J·Evelyn，经伦敦皇家学会批准出版了一部森林志，即《林木论》。在这本著作中，人们可以说是第一次了解到一个现实：当时，在造船业中如此重要的树木的确正在悲惨地遭到浩劫;必须采取紧急措施，通过认真植树以便确保未来有足够的树木。(with...London介词短语作条件状语修饰published，其宾语是a book。在which定语从句中，one泛指人们。a realization是谓语sees的宾语。so important in...ship是非限定性定语，用来修饰trees。句中两个that均引导同位语从句用来揭示realization的概念内涵。).
37.As a magnetic material becomes more and more magnetized，more and more of its magnetic domains line up，with their north poles a11 pointing inone direction and their south poles in the opposite direction.
随着材料的磁性变强，材料中越来越多的磁畴便会排列起来，其N极均指向一个方向， 而S极则指向相反的方向。 (介词复合结构with.一用来对主句中的谓语lineup进行补充说明。).
38.Since the earth is slightly flattened at its poles，the distance of its surface at the north pole or south pole from its center is less than that at the equator.
由于地球的两极略为扁平，所以南北两极地表面离地心的距离比赤道地表面离地心的距离要近一些。(distancefrom..，“离……的距离”。that代替distance。).
39.Solar energy seems to offer more hope than any other source of energy，particularly since those areas most in need of water lie rather close to the equator and have a relatively clear atmosphere.
太阳能似乎比任何其他能源更有希望，尤其是因为这些迫切需要水的地区离赤道很近，那里有较清洁的大气。(lie和have是两个谓语，主语是those areas。most in need of water为介词短语作定语修饰areas。).
40.For a very long time man has been seeking the possibility of combining various metals into alloys with a view to obtaining better materials for given purposes.
长期以来，人们一直在寻找把各种金属熔成合金的可能性，其目的在于为某些用途获得更好的材料。(with。viewto..，“以……为目的”，“为……起见”，是短语介词，引出的介词短语起目的状语作用。) .